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From:   Rick Macklem <rmacklem@uoguelph.ca>
To:     "J. Bruce Fields" <bfields@fieldses.org>
CC:     "Kornievskaia, Olga" <Olga.Kornievskaia@netapp.com>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        "nfsv4@ietf.org" <nfsv4@ietf.org>
Subject: Re: NFSv4.2 server replies to Copy with length == 0
Thread-Topic: NFSv4.2 server replies to Copy with length == 0
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Date:   Thu, 17 Oct 2019 15:55:28 +0000
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>J. Bruce Fields wrote:
>On Thu, Oct 17, 2019 at 02:16:36AM +0000, Rick Macklem wrote:
>> I have now found two cases where the Linux NFSv4.2 server does not
>> conform to RFC-7862. One is as above and the other is a reply to Seek
>> of NFS4ERR_NXIO when the sa_offset argument == file_size (instead of
>> replying NFS_OK along with sr_eof == true).
>
>Huh.  Looks like that's documented behavior of Linux's seek.  (See the
>ERRORS section of the lseek(2) man page.)  Looks like Solaris also
>returns -ENXIO in this case:
>
>        https://docs.oracle.com/cd/E26502_01/html/E29032/lseek-2.html
>
>And freebsd too:
>
>       https://www.freebsd.org/cgi/man.cgi?query=lseek&sektion=2
>
>I wonder where that spec language came from?
Agreed that it is the POSIX draft behaviour.
And, yes, I don't know why the RFC specifies it differently, but when I discussed
it on nfsv4@ietf.org, the concensus was that the RFC indicated a reply
of:
  NFS_OK, sr_eof == true, sr_offset == file_size
for a request of:
  sa_offset == file_size, sa_what == NFS4_CONTENT_DATA
(In the nfsv4@ietf.org archive dated around 2019-08-12.)

>Our NFS server could translate an -ENXIO return into 0 and sr_eof ==
>true easily enough, assuming -ENXIO is really only ever returned in that
>case.
>
>I haven't tested, but from a quick check of the Linux client code I
>think that would require a matching fix on the client side to translate
>sr_eof == 0 *back* to ENXIO.
>
>I don't know if it's worth it.
Yep, agreed. All the FreeBSD client does is what you stated above, mapping
sr_eof == true -> ENXIO for the NFS4_CONTENT_DATA case.

rick
ps: When I re-read it, the comment I made related to Bruce's "wrong" was
      blunt (or maybe rude). I apologize for the tone. All I had intended to
      say was "although it might not be our preferred semantic, it appears
      to clear and implementable, so I do not think it can be "clarified" to
      be the way the Linux server does it". I actually prefer the way the Linux
      server does it, but it is too late now, imho.

--b.